A model pair potential is calculated for Mn-Mn pairs in Al using a Gre
en's function method. The pair potential has a preferred spacing of 4.
7 angstrom. The energy resulting from these Mn-Mn interactions strongl
y favors the Al6Mn, alpha-AlMnSi, and icosahedral quasicrystal structu
res relative to competing simple structures, providing a possible mech
anism for stabilizing the complex structures.